[OpenBIOS] [PATCH 2/4] ppc: add new context handler

[Segher Boessenkool]

On Sun, May 01, 2016 at 11:23:00AM +0100, Mark Cave-Ayland wrote:
> +struct context *switch_to(struct context *ctx)
> +{
> +    volatile struct context *save;
> +    struct context *ret;
> +    unsigned int lr;
> +
> +    debug("switching to new context:\n");
> +    save = __context;
> +    __context = ctx;
> +
> +    asm __volatile__ ("mflr %0\n\t" : "=r" (lr) : : );
> +    asm __volatile__ ("bl __switch_context\n");
> +    asm __volatile__ ("mtlr %0\n\t" : : "r" (lr) : );
> +    
> +    ret = __context;
> +    __context = (struct context *)save;
> +    return ret;
> +}

This isn't correct; GCC is free to put LR-modifying code between
the asm statements.  You should do it in one asm statement.

> +  #ifdef __powerpc64__
> +    #define ULONG_SIZE 8
> +    #define STACKFRAME_MINSIZE 48

The miminum frame size for elfv1 is 112 and for elfv2 is 32.  I think.
But not 48, in any case.


Segher